Intramesangial passage of mononuclear phagocytes in murine lupus glomerulonephritis

By repeated biopsies, time-sequential changes of the injected colloidal carbon distribution were investigated in glomeruli of NZB/W F1 mice. The intraglomerular shift of the carbon, evaluated by counting the particles at several time intervals after carbon injection, demonstrated the movement of the carbon from the glomerular capillaries to the extraglomerular areas. Electron-microscopic examination disclosed that most of the increased cells of the glomeruli were mononuclear phagocytes rich in ingested carbon particles and that extracellular carbon was scarcely present. This strongly suggested that the carbon particles observed at the light-microscopic level reflected those ingested by the phagocytes. The mesangial cells per se scarcely ingested carbon particles. Instead, mononuclear cells, extending their cytoplasmic protrusions toward the dense (immune complex) deposits, were frequently noticed. It is concluded that the mononuclear phagocyte is a principal component of the hypercellular glomeruli, presumably contributing to the scavenging of the mesangium, and also that there is a pathway in the mesangium for these cells to shift from the capillary to the extraglomerular area by way of the vascular pole and lacis area.